Deploying under-utilized landraces in wheat breeding has been advocated to accelerate genetic gains in current era of genomics assisted breeding. Mexican bread wheat landraces (Creole wheats) represent an important resource for the discovery of novel alleles including disease resistance. A core set of 1,098 Mexican landraces was subjected to multi-location testing for rust diseases in India, Mexico and Kenya. The landrace core set showed a continuous variation for yellow (YR) and stem rust (SR) disease severity. Principal component analysis differentiated Mexican landraces into three groups based on their respective collection sites. Linkage disequilibrium (LD) decay varied from 10 to 32 Mb across chromosomes with an averge of 23Mb across whole genome. Genome-wide association analysis revealed marker-trait associations for YR resistance in India and Mexico as well as for SR resistance in Kenya. In addition, significant additive-additive interaction effects were observed for both YR and SR resistance including genomic regions on chromosomes 1BL and 3BS, which co-locate with pleiotropic genes Yr29/Lr46/Sr58/Pm39/Ltn2 and Sr2/Yr30/Lr27, respectively. Study reports novel genomic associations for YR (chromosomes 1AL, 2BS, and 3BL) and SR (chromosomes 2AL, 4DS, and 5DS). The novel findings in Creole wheat landraces can be efficiently utilized for the wheat genetic improvement.

Yellow rust (Puccinia striiformis f. sp. tritici) and powdery mildew (Blumeria graminis tritici) of wheat can be effectively managed by the cultivation of resistant varieties. However, such resistant varieties become susceptible due to evolution and spread of new and matching virulences of these pathogens after a short period of their commercial cultivation. Hence, breeding for disease resistance tends to be a continuous process with prerequisite of identification of diverse resistant donors. In this context, more than 500 genotypes comprising advanced breeding material form CIMMYT and those developed in India were subjected to multilocational screening at hot spot locations of yellow rust and powdery mildew (Dhaulakuan, Malan and Ludhiana) under artificial epiphytotic conditions during the Rabi cropping season 2014-15 to 2016-17. Five genotypes from advanced Indian wheat breeding material were free from both the diseases whereas, 8 genotypes of CIMMYT origin showed mean terminal yellow rust (TYR) severity ≤5S and terminal powdery mildew (PM) reaction ≤3 and were highly resistant whereas 30 genotypes among Indian wheat breeding material showed mean terminal YR severity ≤5S and terminal PM reaction ≤5 were found resistant. Agronomically superior genotypes may be directly utilized as varieties and sources with multiple resistance may be used as donors in breeding program.

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